A Passive Optical Network (PON) technology is a main broadband access technology at present. To resolve a problem that bandwidth is generally limited because a conventional Time Division Multiplexing (TDM) PON is affected by a TDM mechanism, the industry puts forward a Time Wave Division Multiplexing (TWDM) PON system combining a wavelength division multiplexing (WDM) technology and a TDM technology.
The TWDM PON system is a point-to-multipoint communications system. Data transceiving between an Optical line terminal (OLT) at a central office and an Optical Network Unit, (ONU)/Optical Network Terminal (ONT) at premises of a user is performed by using multiple wavelength channels. Each ONU works on one of the wavelength channels. An ONU may indicate an ONU and/or an ONT. In a downstream direction, the OLT uses a downstream wavelength corresponding to each wavelength channel to broadcast downstream data to multiple ONUs that work on the wavelength channel. In an upstream direction, an ONU on each wavelength channel may use an upstream wavelength of the wavelength channel to send upstream data to the OLT in a timeslot allocated by the OLT.
In practical application, to implement a load balance among wavelength channels in the TWDM PON system, a downstream wavelength and an upstream wavelength that are used by an ONU may be dynamically adjusted. When the OLT finds that a wavelength channel is overloaded, the OLT may send a wavelength switching instruction to an ONU that works on the wavelength channel, to instruct the ONU to switch to a wavelength channel with relatively light load by adjusting an upstream wavelength and/or a downstream wavelength of the ONU.
In the current TWDM PON system, in a wavelength switching process of an ONU, the OLT needs to first send a wavelength switching instruction to the ONU, and the ONU performs wavelength switching after receiving the wavelength switching instruction. In a process of waiting for the ONU to complete the wavelength switching, the OLT continuously sends, to the ONU, a query command about whether switching is completed. After completing the wavelength switching, the ONU sends, to the OLT, a message indicating that the wavelength switching is completed. After receiving the message indicating that the wavelength switching is completed sent by the ONU, the OLT starts to send information such as timeslot authorization of downstream data and upstream data to the ONU, and then the OLT and the ONU can restore normal service communication.
In the existing TWDM PON system, in a wavelength switching process, a time for wavelength switching of the ONU is relatively long, and repeated information interaction and confirmation are needed to restore normal data communication between the OLT and the ONU. Therefore, wavelength switching results in a relatively long service interruption time, and consequently user experience for a real-time transmission service such as voice or video may be reduced. In addition, when there is traffic congestion or a large amount of burst data traffic, a data packet loss may occur and service quality may be affected.